The Cell Culture Core supplies high quality cells for the Program Project investigators. The facility is maintained such that it meets and exceeds the relevant federal health and safety standards. The majority of cells provided by the facility are foreskin-derived normal human keratinocytes. These cells are plated with the media, conditions, and density required by each Program Project investigator. Presently the facility is providing over 250 million cells per week to investigators, but it can produce equal to or more than 500 million per week on demand. In addition, the facility has a large library of frozen cells, including transformed and genetically-altered lines, that are available to the investigators. Depending on need, these lines also are maintained at low levels allowing for rapid and efficient boosting of cell numbers at the investigator's request. The facility also routinely produces murine keratinocytes from both normal and transgenic sources, as required for individual Program Project investigators. Dr. Walter M. Holleran, Director, and Ms. Sally Pennypacker, Head Technician, not only provide in vitro culture knowledge and expertise for other investigators, but also insure that health and safety inspections are passed, hoods and incubators are tested and serviced regularly, and cultures are tested monthly for mycoplasma. Both Dr. Holleran and Ms. Pennypacker also possess expertise in working with organotypic cultures, as well as culturing adult skin keratinocytes and fibroblasts, late-passage keratinocytes, basal cell carcinoma cells, fetal rat and mouse keratinocytes, and various explant methods. Core A is developing methods for growth of Hailey-Hailey cells, cell-cell adhesion assays, improved lipid and lamellar body generation, and growth of adult and neonatal murine keratinocytes from various knockout animal models. A fundamental part of the operation of Core A is the interaction between its personnel and members of the Program Project, allowing researchers to obtain high-quality cultures specifically tailored to their needs, while providing direct feedback for optimization of techniques and protocols. The facility is now equipped with amber lights for work with light-sensitive compounds. Finally, Core A provides both maximum numbers of high quality cells and advice on in vitro methods to investigators, who rely heavily on this facility. The continued production of healthy keratinocytes will remain the priority of this key facility.